1. Field of the Invention
The present invention relates to a solid-state image capturing apparatus (e.g., a CMOS image sensor, a CCD image sensor and the like) where lights with different wavelengths are separated and detected by a plurality of light receiving sections laminated in a depth direction of a semiconductor substrate or a semiconductor layer, a method for manufacturing the solid-state image capturing device, and an electronic information device (e.g., a digital camera, a cell phone device equipped with a camera and the like) using the solid-state image capturing apparatus as an image input device for an image capturing section thereof.
2. Description of the Related Art
In a conventional color solid-state image capturing apparatus represented by a CMOS image sensor, a CCD image sensor and the like, on a plurality of solid-state image capturing devices where a plurality of light receiving sections (a plurality of pixel sections) are arranged in two dimensions and in a matrix and the plurality of light receiving sections perform a photoelectric conversion on incident light so as to generate a signal charge, three or four types of color filters are arranged in a mosaic for respective colors so as to correspond to the respective light receiving sections. With this structure, a color signal corresponding to each color filter is output from a pixel section, and the color signal is computationally processed so as to generate color image data which contain other color signals.
However, in a conventional color solid-state image capturing apparatus having color filters for respective colors arranged in a mosaic thereon, about ⅔ of the incident light is absorbed by color filters of three primary colors, for example. Accordingly, in fact, only the about ⅓ remaining incident light can be used for outputting a color signal, thus causing problems of low light utilization efficiency and low sensitivity.
In addition, in a conventional color solid-state image capturing apparatus, a color signal of only one color can be obtained at each pixel section, and also the signal of each of three primary colors needs to be detected at different pixel sections, other color data at the same location (same pixel section) is obtained from color data detected at different pixel sections by computation.
Further, in a conventional color solid-state image capturing apparatus, because a transfer region for signal charges obtained at each light receiving section are arranged on the same surface, it is difficult to enlarge a size of a light receiving regions of each pixel section, leading to a problem of a drop of a light receiving sensitivity that arises from a downsizing of a size of a pixel section (light receiving section).
Conventionally, such problems described above have been dealt with by improving a light receiving characteristic for each unit pixel section. However, such action by improving a characteristic is already reaching its limits due to miniaturization of pixel section's size, and the drop of a light receiving sensitivity described above is causing to prevent a solid-state image capturing apparatus to be further downsized or to have more pixels.
In order to solve these problems, for example, Reference 1 proposes a solid-state image capturing apparatus with a plurality of light receiving sections (charge accumulation sections) corresponding to each color are laminated in a depth direction in a semiconductor substrate, each of the light receiving sections being provided with transfer paths formed by a high concentration impurity region (high concentration diffusion layer). With this structure, color lights with wavelength bands corresponding to depths of a light receiving section are separated and detected at the light receiving section depending on a wavelength dependency of a optical absorption coefficient of a semiconductor, and signal charges of different colors are read out separately via a transfer path formed with high concentration impurity region, so that a plurality of signal charges are read out.
This conventional solid-state image capturing apparatus, which separates and detects lights with different wavelengths by the light receiving sections laminated in a depth direction of a semiconductor layer, has a pixel section cross-sectional structure in which photodiodes (light receiving sections) generating a signal charge for each color light of blue (B), green (G) and red (R), for example, are sequentially laminated from the surface of a light incident side to a deeper direction. According to this conventional solid-state image capturing apparatus, since color separation at each pixel section is taken place employing wavelength dependency of optical absorption coefficient of silicon, there is no need to provide for a color filter above each pixel section. In addition, since signals of the three primary colors are obtained at respective depths in a pixel section, excellent color images are obtained with high sensitivity and high resolution and further without any problem of false colors.
In addition, Reference 2 proposes a solid-state image capturing apparatus, in which a photoelectric conversion section (light receiving section) is provided on a surface of one side of a semiconductor substrate; an inner wall of a trench provided to reach from the other side of the substrate surface to the photoelectric conversion section is covered with a gate insulation film; a readout gate electrode is embedded in the trench; an accumulation diffusion layer for transferring is provided adjacent to the gate insulation film formed on a side of the trench. With this structure, signal charges at the photoelectric conversion section are read out by voltage application to the readout gate electrode embedded in the trench.
In the conventional solid-state image capturing apparatus with this mode, a light receiving section, a readout gate electrode, and an accumulation diffusion layer for transferring, which reads out a signal charge from the light receiving section, are positioned in order from a light incident surface of the semiconductor substrate in a depth direction in its structure so that it is possible for almost all of the image capturing region in the light incident surface to be formed as a light receiving region. Therefore, the light receiving sensitivity is improved by the enlargement of the light receiving region's size, making it possible to downsize the pixel size even more.
Further, Reference 3 proposes a solid-state image capturing apparatus, in which a light receiving section is provided on a back side of a semiconductor substrate; a wiring layer is provided on a front surface of the semiconductor substrate; and a readout transistor for selectively reading out signal charges from a conductive region configuring the light receiving section to the front a pixel forming circuit formed on a surface side of the semiconductor substrate is provided inside the semiconductor substrate. With this structure, for example, a conductive region, configuring a readout gate inside the semiconductor substrate is provided, and signal charges obtained in the light receiving section are read out.
In the conventional solid-state image capturing apparatus with this mode, the amount of charges accumulatable in a photodiode is increased by the structure to have light coming in from its backside, thereby improving a light receiving sensitivity. Further, by forming a transistor and a readout selection line necessary for reading out inside a semiconductor substrate, the number of transistors and wirings formed on the surface of the semiconductor substrate are reduced allowing the pixel size to be miniaturized.
Reference 1: Japanese Laid-Open Publication No. 2004-273951
Reference 2: Japanese Laid-Open Publication No. 2004-281499
Reference 3: Japanese Laid-Open Publication No. 2005-353994